The X-ray CT apparatus emits X-ray using multiple angles around an object, and causes an X-ray detector to acquire the X-ray attenuated by the object. An X-ray beam is shaped in such a way that the X-ray generated in an X-ray tube is transmitted through a bowtie filter, and thereafter, the X-ray beam is emitted to the object. In addition, the X-ray detector is configured so that multiple detector blocks having multiple X-ray detection elements are arrayed in parallel in a rotation direction (hereinafter, referred to as a channel direction) and a rotation axis direction (column direction) of the apparatus.
In a case where the X-ray detector having the multiple detector blocks is used in this way, a clearance is generated between the adjacent detector blocks. Due to this clearance, sensitivity variations occur between the detection element on an inner side of the detector blocks and the detection element on an, end side of the detector blocks. In another case, due to variations in a light receiving area which occur during a manufacturing process of the X-ray detector, the sensitivity variations occur between the respective detection elements. In particular, the sensitivity variations caused by the former factor always occur in a specific detection element, thereby causing a ring-like artifact to appear on an image. In order to restrain these sensitivity variations, the X-ray CT apparatus in the related art performs air correction on measurement data acquired by the X-ray detector.
According to the air correction in the related art, air data scanned in a state where the object is not present is measured in advance, and the air data is referred to as sensitivity of the detection element, thereby correcting a sensitivity variation component included in the measurement data scanned in a state where the object is present.
On the other hand, X-ray exposure affecting human bodies has become an issue in recent years. Accordingly, a technique has been actively studied in order to obtain image quality required for doctor's diagnosis even when scanning is performed by minimizing an X-ray exposure amount (even during low dose scanning). A representative method thereof includes a noise reduction method disclosed in PTL 1.
PTL 1 discloses a method of reducing noise included in measurement data by modelling statistical fluctuations of the measurement data which are caused by an X-ray detection process.